Power consumption of a circuit necessary for modulation and demodulation applied to a recent modulation method becomes increasing steadily. Therefore, technologies for controlling power supply have been developed. Patent literature 1 describes an example of a control circuit which supplies electric power to a circuit receiving a wireless transmission signal through infrared ray. A power supply control circuit described in patent literature 1 includes a light receiving element, an amplification circuit, a signal processing circuit, D/A (digital/analog) converter, an audio amplifying circuit, a speaker, an auxiliary light receiving element, an auxiliary amplification circuit, a microcomputer, a switch, and a power supply, and it operates as follows. An infrared ray signal is photoelectrically-converted by the light receiving element, and a converted electric signal is amplified by the amplification circuit and is inputted into the signal processing circuit. A signal demodulated by the signal processing circuit is turned into an analog audio signal by the D/A converter and is amplified by the audio amplifying circuit to vibrate the speaker. Electric power is supplied by the power supply through the switch to the amplification circuit, the signal processing circuit, the D/A converter, and the audio amplifying circuit. The above-mentioned infrared ray signal is also light-received and photoelectrically-converted by the auxiliary light receiving circuit which is arranged near the light receiving element. The converted electric signal is amplified by the auxiliary amplification circuit and is inputted into the microcomputer. Here, an ON/OFF operation of the switch is carried out depending on the presence or absence of an input signal into the microcomputer. According to this, it is controlled to supply power for the light receiving element, the amplification circuit, the signal processing circuit, and the D/A converter which are used for demodulation from the infrared ray transmission signal to the audio signal.